The invention relates to a pilot-operated pressure shut-off valve which, when an upper system limit pressure is reached in a hydraulic system having a hydraulic accumulator, connects an inlet feeding the hydraulic system to an outlet to a tank and separates this connection when removal of hydraulic fluid from the hydraulic accumulator has caused the system pressure to drop to a lower system limit pressure and which has a main control piston and, in order to control the main control piston, a pilot valve arrangement having two pilot pistons and two pilot springs, the adjustment of which makes it possible for the upper system limit pressure and the lower system limit pressure to be set independently of each other.
A pilot-operated pressure shut-off valve of this type is disclosed, for example, in DE 41 12 065 A1 or in DE 36 08 100 C2. In the case of the pressure shut-off valve according to DE 41 12 065 A1, the pilot valve arrangement comprises two complete pilot valves having a respective valve housing, having a pilot piston in a bore of the valve housing and having a pilot spring which is situated in a spring space and the prestress of which can be changed with the aid of a setting screw. The two pilot valves are placed one above the other onto the housing of the main stage. This pressure shut-off valve has a fairly large construction and is relatively expensive.
In the case of the pressure shut-off valve according to DE 36 08 100 C2, the pilot valve arrangement only has one valve housing. In the latter, two valve bores, each of which accommodates one of the two pilot pistons, run at a distance from and parallel to each other. The two pilot springs are accommodated next to each other in an extension of the valve bores in a cover fitted onto the valve housing of the pilot valve arrangement. The pilot valve arrangement in this pressure shut-off valve still has a fairly complex construction.
There are also pilot-operated pressure shut-off valves in which the pilot valve arrangement has just one pilot piston and one pilot spring and an adjustment of the one system limit pressure always also involves an adjustment of the other system unit pressure. The difference between the two limit pressures is a percentage of the upper system limit pressure, this percentage depending on the size of a surface difference on the pilot piston and on the prestress of the pilot spring. A pilot-operated pressure shut-off valve of this type, in which the upper system limit pressure and the lower system limit pressure cannot be set independently of each other, is disclosed, for example, in the applicant's specification sheet RD 26 411/03.98.